The expansion of tobacco to give it improved filling power per unit weight, i.e. greater volume/g, can be effected in a number of known manners. Most generally, however, it is accomplished by impregnating the tobacco, for example in the form of cut filler, with an impregnating agent or agents and then subjecting the impregnated material to rapid heating, to drive off or volatilize the impregnant thereby causing expansion of the tobacco. Heating conveniently can be effected in a stream of hot gas flowing through a pneumatic conveying column, commonly referred to as a "tower". Following heating in the tower, the tobacco is separated from the gas stream, the separation of the product heretofore being accomplished with a cyclone separator.
U.S. Pat. No. 3,771,533 discloses the impregnation of tobacco filler with ammonia and carbon dioxide as expansion agents. The impregnated tobacco material is subjected to rapid heating, for example with a stream of hot air or air mixed with superheated steam, whereby the tobacco is puffed as the impregnant is converted to a gas.
Belgian Pat. No. 821,568 and pending U.S. application Ser. No. 822,793 disclose methods for impregnating tobacco with liquid carbon dioxide, converting a portion of the impregnant to solid form and then rapidly heating the impregnated tobacco to volatilize the carbon dioxide and puff the tobacco.
Pending U.S. application Ser. Nos. 891,290 and 891,468 each disclose impregnation of the tobacco with gaseous carbon dioxide under pressure and then subjecting the tobacco to rapid heating after pressure reduction. All aforementioned methods disclose effecting expansion of the tobacco in a tower with a flow of heated gas, with separation of the expanded tobacco from the gas stream being achieved in a cyclonic separator.